Battery inconsistency is a problem which always cannot be completely solved in current battery applications, particularly battery group applications.
Batteries are generally used in groups, several and dozens of batteries are used in groups at least, and hundreds of or even thousands of batteries are used in groups. The inconsistency among various batteries in a battery production link absolutely exists due to multiple factors such as a manufacturing process problem, material non-uniformity, incompletely identical density/mass of energy storage substances and the like. In a battery using link, an environmental temperature of each battery during charging and discharging is different due to non-uniformity of heat fields during charging and discharging of battery packs since batteries have different positions in the battery packs after the batteries are packed. The inconsistency may be gradually enlarged and even out of control in the battery using link, i.e., out-of-control overcharge and undercharge may occur during charging, and an overdischarge phenomenon of partial batteries is intensified during discharging. A discharge depth of each battery in the battery pack is inconsistent, wherein one part of batteries may be in an overdischarge state, and partial available remaining electric quantity is not used in the other part of the batteries, so that overall discharge capacity of the battery pack is decreased and overall cycle life of the battery pack is accelerated to decrease along with decrease of cycle life of one part of batteries with a maximum discharge depth, thereby causing early scrap of the battery pack. However, part of batteries in an available state are scraped together to cause waste when the whole battery pack is replaced.
In addition, overcharge even may cause explosion and fire accidents.
Therefore, an existing battery pack power system needs to be equipped with a battery management system. A current battery management system has two technical solutions for eliminating inconsistency of the batteries (i.e. balancing of the battery pack). One solution is an energy-consuming type solution, i.e., externally connecting a battery with the maximum remaining electric quantity with a resistor to reduce the remaining electric quantity of the battery. The other solution is an electric energy transfer solution among batteries, i.e., performing electric energy transfer among the batteries and charging a battery with the minimum remaining electric quantity by using the battery with the maximum remaining electric quantity or charging the battery with the minimum remaining electric quantity by using the battery pack and a DC-DC converter. Defects of the former solution are as follows: energy of the batteries is wasted, endurance of the battery pack is reduced and the heat field of the battery pack is more non-uniform and unexpected, while the latter solution cannot be implemented without the DC-DC converter. However, extra electric energy consumption of the battery pack is increased due to conversion efficiency of the converter.
For a battery pack power system equipped with various power generation devices, usage of the power generation devices is basically at a high-voltage level for converting an output voltage of the power generation devices into a battery pack voltage, and then the battery pack is charged. Due to the inconsistency of the batteries, the electric quantity charged into each battery is unbalanced, and then the batteries are subjected to various balancing by using an existing balancing technology, causing electric energy waste. Particularly for a movable or offline battery pack power system, the electric energy waste means decrease of endurance of the battery pack.
Due to the existence of the inconsistency of the batteries, batteries of the same brand, the same specification, the same batch and the same sorting standard may be selected as much as possible during sorting and packing of the batteries to reduce inconsistent indexes among the batteries as much as possible, thereby increasing sorting cost of the battery pack and further increasing purchasing cost of the battery pack.
In recent years, a charging apparatus for independently charging the batteries in the battery pack appears. Although the apparatus is not popularized and applied on a large scale, a qualitative difference is made compared with a former traditional series charging technology in general application. Tests discover that the above independent charging apparatus and technology still have defects as follows: a discharge link cannot be controlled, and all batteries in the battery pack cannot be guaranteed to have the same discharge depth; as a certain distance exists between a charger and the battery pack, line diameter specifications and quantities of charging lines are correspondingly increased; laying (including shielding) of high-current charging lines and data collection lines increases an extra space, cost and unsafe factors; and moreover, a long-distance data collection line reduces data collection precision.
An existing charging method generally takes “full charging” as a single objective, and under the objective, due to the inconsistency among the batteries, the traditional series charging manner may cause that some batteries in the battery pack are in overcharge and overdischarge states during charging or discharging. When the battery pack is charged by using a charger capable of independently charging each battery, an overcharge phenomenon of the battery pack can be avoided, while a phenomenon that some batteries have a large relative discharge depth, i.e. a relative overdischarge phenomenon, in the discharging process still cannot be avoided.
A Chinese patent literature with an application publication number of CN102214938A discloses a charging control method for a rechargeable battery used for a portable computer. The charging control method comprises: acquiring a charging current control parameter of the rechargeable battery; modifying charging current of the rechargeable battery from a first charging current to a second charging current smaller than the first charging current according to the charging current control parameter; and charging the rechargeable battery by using the second charging current, thereby prolonging service life of the rechargeable battery.
A Chinese patent literature with an application publication number of CN104052136A discloses a battery pack, a charging circuit and a charging apparatus.
The battery pack comprises battery blocks and a memory, wherein the battery blocks comprise battery cells; the memory stores battery information; the battery information comprises lower limit voltages of the battery blocks set according to models of the battery blocks; the charging circuit comprises a voltage measurement unit and a control unit; and the voltage measurement unit is configured to measure inter-terminal voltages of the battery blocks, and the control unit is configured to control charging according to the inter-terminal voltages measured by the voltage measurement unit.
A Japanese patent literature with an application publication number of JP2008-220110 relates to a battery pack, a charging method and a charging system. Charging current specified by a charging voltage specified value is decreased under conditions that a maximum battery cell voltage in battery cell voltages measured from each of a plurality of battery cells is compared with a full charging voltage and the maximum battery cell voltage is higher than the full charging voltage. In addition, the charging current specified by the charging voltage specified value is increased under conditions that the maximum battery cell voltage and the full charging voltage are compared and the maximum battery cell voltage is smaller than the full charging voltage. Charging of a degraded battery to an overcharge area is prevented by using a charging method for periodically controlling during a charging period when such a charging voltage specified value is changed.
An international patent with an application publication number of WO2013/173195 discloses a charging system of a battery pack for an electric vehicle. The charging system comprises: a charging station electrically coupled to the battery pack, and configured to transfer charging energy to an energy storage system in a first operating mode at a maximum quick charging rate and transfer the charging energy to the energy storage system in a second operating mode at a lower charging rate; a data collection system, configured to acquire a set of data indicating state of charge (SOC) of the battery pack and one or more expected charging optimization parameters; and a station control, configured to respond to the set of the data and the expected charging optimization parameters and automatically establish a charging configuration file used for the battery pack to enable a control signal to be effective and operate the charging station in the second operating mode or enable the control signal to be effective and operate the charging station in the first operating mode.